Process for bleaching textiles



S. H. MHA-TRE FOR BLEACHING TEXTILES Filed July 18, 1967 i m Q QN Q Qwww5@ Inventor A Horne y United States Patent O 3,544,261 PROCESS FORBLEACHING TEXTILES Shamrao Harischandra Mhatre, Madras, India, assignorto The Buckingham & Carnatic Limited, Madras, India, a public company ofIndia Filed July 18, 1967, Ser. No. 654,119 Claims priority, applicationGreat Britain, July 22, 1966, 33,044/ 66 Int. Cl. D06l 3/06 U.S. Cl.8-108 3 Claims ABSTRACT OF THE DISCLOSURE A process for bleachingtextile materials of natural and/or synthetic fibers in the form ofyarn, webs, woven and non-woven fabrics, filaments, and the like inwhich the textile material is impregnated with an aqueous hypochloritebleaching solution having an active chlorine content of about 0.25-10grams/liter and a pH of about 7-12. The impregnation is conducted so asto provide on the textile material a concentration of chlorine of about0.-06l.0% by weight of the textile material. The impregnated textilematerial is then exposed to an atmosphere of saturated or supersaturatedsteam at a temperature of about 50-140 C. for a period of about 15-60seconds. The bleached material is then subjected to washing and drying.

The proposed process is an improvement over the known process ofbleaching textiles using sodium or calcium hypochlorite solution aloneor in admixture with other substances. The conventional practice ofbleaching consists of impregnating textiles in a hypochlorite solutionand storing it until bleaching is complete. The same practice isfollowed while using the hypochlorite in admixture with othersubstances. This is a time consuming process and involves the use of aI-box or a timing wheel in the rope form or open width where the fabricis subjected to considerable crushing which may lead to shadow creases.This is a serious disadvantage if the fabric or web or any other textilematerial is to be subsequently dyed. The conventional process is alsolimited to a narrow range of useful pH, viz 9.5 to 10.5 in that at pHvalues below 9.5 the risk of degradation of cellulose is a seriousfactor and at pH values above 10.5 a satisfactory level of whiteness isnot produced.

The object of this invention is to improve the conventional process soas to complete the bleaching within a relatively short period. Time forbleaching can in fact be reduced to the order of a few seconds from thatof few hours as at present.

It is proposed according to this invention that the treatment oftextiles with a hypochlorite or a hypochlorite in admixture with othersubstances be conducted in an atmosphere of steam. This process which iscarried out in open width in the case of fabrics, webs or tapes can alsobe rendered truly continuous in that further bleaching, washing anddrying or any other treatment can be carried out in a composite unit sodesigned for the purpose.

It is found that very little active chlorine is left behind on thefabric or web or yarn in the proposed process, the advantages resultingthereby being:

(l) avoidance of the risk of after-tenderin g (2) elimination of thenecessity for anti-Chlor treatment.

Broadly speaking the process is carried out as under: The textilematerial which is in the grey state, or scoured or desized state, istreated, conveniently at room temperature, with either sodiumhypochlorite or calcium hypochlorite solution (aqueous) or both, with orwithout other additives such as wetting agents or chelating agents3,544,261 Patented Dec. 1, 1970 ice such as ethylenediamine tetraaceticacid and diethylenetriamine pentaacetic acid or sodium chloride orsodium bromite, or other catalyst and/ or accelerator for the purpose,proprietary or otherwise, squeezed to give the required pick-up ofbleaching agent, and then heated under steam when in a few seconds thebleaching action is completed.

For treating with bleaching solution the textile material, dry or wet,is passed through a pad or mangle containing the bleaching solutionmaintained at a desired pH, ranging from 7 to 12, and at roomtemperature. It is subjected to the benefit of one or more nips soadjusted to give the desired resultant pick-up of bleaching agent.Usually the pick-up of 45 to 100% of the bleaching or of 0.05 to 1.0% ofactive chlorine on the weight of the textile material is desirable. Forheating under steam the so treated material is exposed to the action ofeither saturated or superheated steam in a chamber or a pressure vessel,which is also referred to as agen The value of this temperature mayrange from 50 C. to 140 C. For temperature ranges above D C., thetextile material (after impregnating With the said bleaching solution,with or Without additives), lmay be preheated in a preheater using steamor infrared or direct heat radiations just prior to steaming in the mainchamber.

It is observed that under the aforesaid conditions the bleaching actionis completed within l5 to 60 seconds.

Concentration of bleaching solution is preferably from 0.25 to 10.0gms/1. of active chlorine.

The present invention also proposes a plant for bleaching using theforegoing process.

Basically the plant will comprise of an impregnating chamber for thebleaching solution and a steam chamber or ager with means to conveytextile material from the former to the latter and means to remove thebleached textile material from the steam chamber.

In a preferred embodiment a pre-heating chamber is included in the plantprior to conveying the impregnated textile material to the steamchamber.

According to a further embodiment the plant comprises an impregnatingchamber, a steam pre-heating chamber, a second impregnating chamber andsteam chamber for completing bleaching.

Also included in a plant for carrying out the process of this inventionmay be (i) a washing machine into which textile material is conveyedfrom the steam chamber, and (ii) drying means. Drying means may be aseries of heated cylinders or a hot air chamber.

Means for expressing the textile material after impregnation as well asafter washing are also preferably included in the plant according tovarious embodiments.

A pad or mangle, with or without an auxiliary saturator is used as animpregnation chamber so that material to be treated with bleachingsolution can be given the benefit of one or more impregnations and nipsto impart requisite pick-up of bleaching agent.

It is found that the degradation of cellulose in the textile materialbleached by the process herein described, as determined by the fluidityvalues in a cuproammonium solution, is lessor comparable to that of thesame textile material treated by the conventional process. It is alsofound that the degree of whiteness as determined by visual inspection ofthe bleached textile material or the reflectance values as measured byany of the standard instruments for the said purpose for the materialbleached by the herein proposed process is equal or superior to thatproduced by the conventional process and that the tensile strength, bothfor the warp and weft, of the textile material bleached in accordancewith this process is equal or superior to that of the textile materialbleached in the conventional marmer.

The results of comparative tests done on four sets of cotton materialbleached (i) by the herein proposed process and (ii) by the conventionalprocess are given below:

EXAMPLE Identical samples of textile material, as given in the followingTables I and II, were treated by conventional as well as herein proposedbleaching methods.

For conventional process a sodium hypochlorite solution in watercontaining 2 grams per litre of available or active chlorine at a pHbetween l-10.5 at 30 C. was used. The period for which the materialstayed in contact with the bleaching solution was 45 minutes.

'For the herein proposed process also sodium hypochlorite solution inwater containing 2 grams per litre of available or active chlorine wasused. The pH of the bleaching solution was kept at `8.5i0-25. Thetextile material was drawn through the impregnating chamber at the rateof 55 meters per minute so that total contact time thereof with thebleaching solution was l2 seconds. The bleaching solution was kept atroom temperature. Temperature in steam treatment chamber was between 95and 98 C.

TABLE I Fluidity Conventional New Quality process process Drill (8.1ozs./sq. yd.):

TABLE II [Tensile strengths (lbs.) process] Conventional Herein proposedSample No. Warp Weft Warp Weit Size of test strip was 7" x 4" andmachine used was Goodbrand Machine.

The invention is described below with reference to the accompanyingdrawings.

In the drawings:

FIG. 1 shows a plant which will be needed to carry out the process inits broadest sense.

FIG. 2 shows more comprehensive plant in accordance with this invention.

Referring to FIG. 1 the impregnating box is marked 1 and has a series ofrollers 11 around which the textile material 10 passes and getsimpregnated with the bleachprovement which comprises:

ing solution contained in the box 1 and gets nipped by the nippingroller 12 to the desired amount of pick-up from Where it passes on tosteam treatment chamber or ager 3 having a set of rolls 16. Steam,superheated or saturated, is injected into the chamber 3. The speed atwhich rolls 11 and 16 rotate is adjusted to provide time required forproper impregnation and duration of steam treatment.

In FIG. 2 the textile material 10, from the rst impregnating chamber 1after passing around a set of rollers 11 is nipped at rollers 12 andconveyed by the nipping rollers and roller 13 into preheating chamber 2where after passing over a set of rollers 14 it is conveyed by rollers15 into the second impregnating chamber 3. After passing over sets ofrollers 16 in chamber 3, the textile material is nipped at rollers 17and conveyed into steaming chamber or ager 4 where the textile materialis nally bleached. From chamber 4 after passing over the rollers 19 thebleached material is nipped at rollers 20 and conveyed therefrom to awashing machine having three compartments 5, 6 and 7 with a series ofrollers 21 for passage of the material through the compartments 5, `6and 7 of the washing machine, and rollers 22, 23 for nipping. Nippingrollers 23 and rollers 24 convey the bleached and washed material todrying means 8 comprising a series of heated rollers 9 after passingaround which the bleached, washed and dried material 10 is taken o aroller 25. If desired, a preheater 26 with rollers 27 may be employed inconjunction with steam chamber 2.

What We claim is:

1. In a process of bleaching a continuous strip of textile material witha hypochlorite solution, the imdrawing said material through an aqueoushypochlorite bleaching solution having a chlorine content of about0.25-10 grams/liter and a pH of about 7-12, the rate of movement of saidmaterial through said solution being such as to impregnate said materialwith about (10S-1.0% of chlorine by weight of said material; exposingsaid resultant impregnated material for a period of about 15-60 secondsto an atmosphere of saturated or supersaturated steam at about 50-140 C.and washing and drying said material.

2. A process according to claim 1 in which the chlorine content of saidhypochlorite solution is about 2.0 grams/liter and the pH about 8.5, andthe rate of movement of said material through said hypochlorite solutionis such as to expose it to said solution for a contact time of about l2seconds.

3. A process according to claim 2 in which the bleaching solution is atroom temperature and the resultant impregnated material is subjected topreheating prior to exposure to an atmosphere of saturated orsupersaturated steam.

References Cited UNITED STATES PATENTS 1,754,909 4/1930 Schwalbe et al.8-108 MAYER WEINBLATT, Primary Examiner U.S. Cl. X.R. 8-l08.5

